The catalytic preparation of hydrocarbons from synthesis gas, i.e. a mixture of carbon monoxide and hydrogen, is well known in the art and is commonly referred to as Fischer-Tropsch synthesis.
Catalysts suitable for use in a Fischer-Tropsch synthesis process typically contain a catalytically active metal of Group VIII of the Periodic Table of the Elements (Handbook of Chemistry and Physics, 68th edition, CRC Press, 1987-1988) supported on a refractory oxide, such as alumina, titania, zirconia, silica or mixtures of such oxides. In particular, iron, nickel, cobalt and ruthenium are well known catalytically active metals for such catalysts. Reference may be made to EP-A-398420, EP-A-178008, EP-A-167215, EP-A-168894, EP-A-363537, EP-A-498976, EP-A-71770 and WO-99/34917.
In the Fischer-Tropsch synthesis, as in many other chemical reactions, the supported catalyst, the reactants and a diluent, if present, in contact with one another usually form a three phase system of gas, liquid and solid. Such three phase systems may be operated, for example, in a packed-bed reactor or in a slurry-bubble reactor. A packed-bed reactor may comprise a packed bed of solid catalyst particles through which there is a flow of gaseous and liquid reactants. A slurry-bubble reactor may comprise a continuous phase of liquid with the solid catalyst suspended therein and gaseous reactants flowing as bubbles through the liquid. In all such operations it is important that the supported catalyst is mechanically strong, so that the catalyst particles maintain their integrity through the entire operation. The stronger the catalyst support or the supported catalyst, the higher a catalyst bed may be in a packed-bed reactor or the longer the residence time of the catalyst may be in a slurry-bubble reactor.
Further, there is a continuous interest in finding catalysts for use in the Fischer-Tropsch synthesis which provide an improved activity and an improved selectivity in the conversion of carbon monoxide into valuable hydrocarbons, in particular hydrocarbons containing 5 or more carbon atoms (“C5+ hydrocarbons” hereinafter), and minimise the formation of carbon dioxide, which is a carbon containing by-product of low value, or even negative value.